[m-dev.] [reuse] diff: easy radical alias widening

[Nancy Mazur]

Hi,


===================================================================


Estimated hours taken: 1

If the aliases get too big, there is no use in really trying to spend
hours and hours making computations with them... A drastic widening
is added (when the size of the alias-set exceeds a certain size, give
up, and throw a top abstract substitution). 
At some point the widening should become less drastic. 

pa_alias_as.m:
	Each time one computes a new set of aliases, test whether
	the set becomes too big or not. If zo, set the alias to top. 


Index: pa_alias_as.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/Attic/pa_alias_as.m,v
retrieving revision 1.1.2.7
diff -u -r1.1.2.7 pa_alias_as.m
--- pa_alias_as.m	2000/10/23 07:31:35	1.1.2.7
+++ pa_alias_as.m	2000/11/23 14:59:12
@@ -176,8 +176,10 @@
 
 % constants
 :- func alias_limit = int. 
+:- func top_limit = int. 
 
-alias_limit = 100000.
+alias_limit = 100.
+top_limit = 1000.
 
 %-----------------------------------------------------------------------------%
 
@@ -402,6 +404,10 @@
 	; 
 		Alias0 = real_as(_), 
 		(
+			size(Alias0) > top_limit
+		->
+			top("Size too big", Alias)
+		;
 			size(Alias0) > alias_limit
 		-> 
 			normalize_with_goal_info( ProcInfo, HLDS, GoalInfo, 
@@ -418,7 +424,8 @@
 		(
 			A2 = real_as(OLD)
 		->
-			pa_alias__extend(ProcInfo, HLDS, OLD, NEW, Aliases),
+			pa_alias__extend(ProcInfo, HLDS, 
+				OLD, NEW, Aliases),
 			wrap(Aliases,RESULT)
 		;
 			A2 = top(_)
@@ -840,6 +847,11 @@
 		LIST = []
 	->
 		AS = bottom
+	;
+		list__length(LIST,Length), 
+		Length > top_limit
+	->
+		top("Size too big", AS)
 	;
 		AS = real_as(LIST)
 	).

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